A high oxygen pressure is requited in growing single crystal NiZn ferrite of a stoichiometric composition by the Bridgman method. As pointed out in a previous paper, the oxygen pressure could be lowered by partial substituting of NiO with MnO. The relationship between the amount of MnO substitution and the oxygen pressure required in growing single crystals of NiZn ferrite having about 50 mol% of Fe
2O
3is investigated. In single crystals of NiZn ferrite containing 6 mol% MnO (NM 6), an oxygen pressure of 100 Kg/cm
2is required, while those with 8 mol% MnO (NM 8) requite 50 Kg/cm
2oxygen pressure and a 12 mol% MnO (NM 12), 1 Kg/cm
2oxygen pressure. Magnetic permeability of the single crystals before annealing at 50 MHz was 100 for NM 12, 120 for NM 8, and 130 for NM 6; with

cm and B
20> 3300 G.